The present invention relates to an eyeglass lens processing apparatus for beveling a periphery of an eyeglass lens to be fitted in an eyeglass frame.
Eyeglass lens processing apparatuses are provided with a beveling tool such as a grindstone having a V groove (bevel groove) for forming a bevel on a periphery of a rough-edged eyeglass lens. Moreover, in recent years, more and more eyeglass frames have a sharp curve, and high-curve lenses whose the curves of the refractive surfaces are sharp are used. When the bevel is formed on the high-curve lens, the use of the large-diameter beveling grindstone having the V groove causes a so-called bevel thinning (a phenomenon in which the height or the width of the bevel is small). As solutions thereto, the following are proposed: an apparatus having a beveling grindstone that separately forms a front bevel on the lens front side and a rear bevel on the lens rear side (Japanese Unexamined Patent Application Publication No. 2008-254078 [corresponding to US 2009011687]); and an apparatus having a small-diameter beveling grindstone (Japanese Unexamined Patent Application Publication No. 2005-74560 [corresponding to EP 1510290]).
In related beveling tools such as beveling grindstones, as shown in FIG. 1, a processing surface Vrk for forming a rear bevel foot (rear side lens edge coupled to the rear bevel) LVrk coupled to the rear bevel LVr on the lens rear side has a constant inclination angle with respect to the x-axis direction of a lens chuck shaft. FIG. 1 is a structural view of grindstones shown in Japanese Unexamined Patent Application Publication No. 2008.254078, and illustrates an example of beveling grindstones that separately form a front bevel LVf and a rear bevel LVr of a high-curve lens. A processing surface Vr for forming the rear bevel LVr and the processing surface Vrk for forming the rear bevel foot LVrk are integrally formed on a rear beveling grindstone GVr. The inclination angle αk of the processing surface Vrk with respect to the x-axis direction is constant from the point Ps of border with the processing surface Vr to the endpoint Pe. That is, the increase rate of the distance to the processing surface Vrk from a line Xs parallel to the x-axis direction and passing through the border point Ps is constant. For example, the inclination angle αk is 15 degrees, and is set as an angle necessary for avoiding the interference between the bevel foot and the rim of the eyeglass frame when the lens having the bevel formed thereon is held by the rim. Moreover, importance is placed on the appearance of thin-edge lenses. However, when a thick-edge lens is processed with the beveling grindstone GVr thereafter, the edge largely protrudes rearward and looks thick. In particular, in the case of high-curve lenses, the edge of the rear bevel foot LVrk is rather sharp, and the sharp edge readily touches the user's cheek.
An example of a method of thinning the edge on the lens rear side is to additionally perform chamfering. However, a large chamfer for rendering the edge look thin requires a skill and time when it is made by hand, and an inexperienced worker cannot make a good-looking chamfer. Although there is a method in which a chamfering mechanism having a chamfering tool is provided in the apparatus, not only an extra time is required for the chamfering process but also the apparatus is complicated and the price of the apparatus is high. Moreover, for high-curve lenses, the accuracy of estimation of the angle part position of after the bevel foot formation is low, so that by a method based on the estimation of the angle part position, chamfering as planned is difficult to perform.